The overall objective of this proposed research is to study the role of the Q and TL subregions of the murine histocompatibility complex in differentiation and development. These genetic regions encode for cell surface molecules with characteristics very similar to those involved in cell-cell communications during an immune response. The specific aims for the next five years are as follows: (1) to continue our study of the ontogeny of the class I antigens determined by the Q and TL subregions; (2) to determine the influence of the Q and TL subregions on early embryonic development; (3) to determine the relationship between t-mutant genes and Q/TL genes; (4) to investigate the regulation of expression of the Qa/TL genes; and (5) to continue to production of genetic tools necessary for the continued investigation of the Q and TL subregions. Techniques to be used include cytotoxicity and ELISA techniques, Northern blot analyses, hematopoietic assays, transfection experiments, production of transgenic mice, analysis of the in vivo effects of monoclonal antibodies, genetic complementation tests, in vitro expression studies, and the production and analysis of new congenic strains of mice.